Cathode ray tube with electron beam interceptor



O 28, 1969 J. H. CALDWELL ETAL 3,475,537

CATHODE RAY TUBE WITH ELECTRON BEAM INTERCEPTOR v Filed Oct. 6, 1967 FIG. I

INVENTORS JOHN H CALDWELL CHARLES W. KLEE ALEXANDER J. H/LLER ROBERT H. MATHES THRE E HANLEY- l I. M nopmgys United States Patent O 3,475,637 CATHODE RAY TUBE WITH ELECTRON BEAM INTERCEPTOR John H. Caldwell IV, Hyattsville, Md., Charles W. Klee, Washington, D.C., and Alexander J. Hiller, Oxon Hill, Thure E. Hanley, Temple Hills, and Robert H. Mathes, Oxon Hill, Md., assignors to the United States of America as represented by the Secretary of the Navy Filed Oct. 6, 1967, Ser. No. 674,061 Int. Cl. H01j 31/02 US. Cl. 313-72 4 Claims ABSTRACT OF THE DISCLOSURE A cathode ray tube in which an electron beam collector is provided to obstruct the electron path while the beam is at its rest position prior to scanning the screen. The purpose of the electron beam collector is to prevent luminescence of the screen while the beam is at its rest position, thus permitting photographic recording of single sweep traces while eliminating unwanted fogging of the film otherwise caused by luminescence from the stationary electron beam.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION The present invention relates generally to cathode ray tubes and more particularly to an improved cathode ray tube capable of displaying single sweep traces in a manner suitable for recording on photographic film. When the phenomeonon being displayed on a cathode ray tube is not repetitive in nature, it becomes necessary to record single sweep traces and this then complicates the task of recording such traces due to the difficulty in getting enough light to the film. By optimizing the cathode ray tubes phosphor type and its accelerating voltage as well as the cameras lens speed and object-to-image ratio and the film speed in an attempt to increase the amount of light to the film, the sensitivity of the system to unwanted light is also increased. The greatest source of unwanted light is the unmoving luminescent spot caused by the electron beam while in its reference position as it waits to sweep across the screen. The stationary electron beam causes phosphorescence at one spot on the screen which produces a glow across the entire screen which is sensed by the photographic film and as a result, the film becomes fogged to an extent which obscures the desired trace. Camera shutters cannot be made to operate at speeds which approach the speed of a single oscilloscope sweep. Therefore it is not possible to eliminate the unwanted light by synchronizing the camera shutter with the sweep. Consequently single sweep photography involves manually opening the camera shutter, triggering one sweep of the oscilloscope, and hten closing the shutter. By this procedure, the shutter is open for a period of time much longer than than the duration of a single sweep and the film is vulnerable to unwanted light such as that caused by the waiting electron beam. In the past, attempts have been made to electronically blank the electron beam by applying an electronic potential across the cathode and grid to bias the tube beyond cut-off, thus maintaining a dark screen during the waiting time. The electronic blanking has not been altogether satisfactory, particularly at fast sweep rates, because the oscilloscope intensity control must be almost fully advanced in order to obtain a trace which is bright enough to be recorded on the film,

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which then results in the creation of unwanted light by the waiting electron beam.

SUMMARY OF THE INVENTION The general purpose of the present invention is to provide an improved cathode ray tube having means incorporated therein for eliminating a spot of light normally caused by a stationary electron beam as it waits to be triggered from its rest position to sweep across the screen. The present invention accomplishes this purpose by providing an electron beam collector so positioned within the cathode ray tube so as to intercept the electrons when said electron beam is in its rest position.

An object of the present invention is to provide a cathode ray tube suitable for use in photographic recording of single sweep traces displayed on said tube.

Another object of the present invention is to provide a cathode ray tube having a positive means for eliminating the spot of light normally caused by an electron beam while it is maintained in its rest position prior to being triggered to scan the screen.

A further object of this invention is to provide a cathode ray tube suitable for photographic recording of nonrepetitive events which are to be measured and displayed on said tube.

Other objects and advantages of this invention will be readly appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIGURE 1 is a diagrammatic view showing a cathode ray tube constructed in accordance with a preferred embodiment of the present invention and shown in axial section.

FIGURE 2 is a sectional view taken on the line 2-2 of FIGURE 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, a cathode ray tube, shown generally at 11, is comprised of a neck portion 12, a funnel section 13, a viewing screen 14 and a base 15 for electrical connection of the tube into a tube socket. Positioned within the neck portion of the tube is an electron gun 16 shown generally by the brackets. The electron gun consists of an emitter 17 having a cathode, a heater, and a control grid. The electron gun also includes a focusing electrode 21 to converge the electrons into a thin beam 28 and further includes an accelerating electrode 22 to increase the speed of said electrons. Positioned within the cathode ray tube axially downstream of the electron gun is a first pair of deflection plates 23 and 24 to cause horizontal deflection of the electron beam. Also positioned axially downstream of the electron gun is a second pair of deflection plates 25 and 26 to cause vertical deflection of the electron beam on the screen 14.

When using a cathode ray tube of the type described to display a single sweep trace of a non-repetitive event, one pair of horizontal deflection plates is normally used to position the electron beam in a rest position on one side of the screen 14 and to sweep the electron beam across the screen when the event occurs. :While the beam is swept across the screen, the signal to be measured is applied to the other pair of deflection plates. To eliminate the undesired spot of light normally produced by the electron beam in its rest position, the present invention incorporates an electron beam collector 27 which is so positioned within the cathode ray tube as to obstruct the path of the electrons while the electron beam is in said rest position. The electron beam collector is made of an electrically conductive material and is preferably formed in the shape of a cone for greatest efliciency. The electron collector preferably has an electrical potential applied thereto of a magnitude approximately equal to that of the immediately surrounding area within the tube but slightly positive with respect thereto to assist in the collection of electrons without disturbing the electrical potential within the tube. For best results, the electron beam collector 27 is radially displaced from the axis of the tube and is positioned in the proximity of the second pair of deflection plates to intercept the electron flow and create a shadow area 29 on the screen which remains dark at all times. The cathode ray tube of this invention enables the shutter on the camera to be open while the electron beam is in its reference position without causing any fogging of the photographic film because the electron beam collector 27 intercepts the flow of electrons to the screen 14 when the electron beam is in its rest position. When the event to be recorded occurs, the sweep circuit is triggered and the electron beam is caused to scan the screen while the signal across the deflection plates 23 and 24 produces the trace on the screen. The electron beam collector 27 does not interfere with the production of the sweep trace on the screen but only intercepts the electrons while the electron beam is directed to its rest position.

It may be seen therefore that the present invention provides a positive means for preventing phosphorescence of the screen while the electron beam is held in its rest position. The present invention therefore makes possible the photographic recording of a single sweep trace without interfering with the formation of said trace. The cathode ray tube of this invention is considered to be a substantial improvement over prior devices incorporating electronic blanking circuits for the reason that the electronic blanking circuits operated to either position the electron beam off of the screen and onto the walls of the funnel portion 13 of the cathode ray tube, or alternatively to bias the electrodes to the point of cutting oif the electron beam. Each of these electronic approaches have disadvantages in that, if the electron beam is deflected against the funnel portion of the cathode ray tube, the electrons reflect from that wall and impinge upon the screen to cause phosphorescence and also secondary electron emission is caused when the electrons strike the funnel wall. The secondary electrons also produce phosphorescence which results in fogging of the photographic film. If the electrodes of the cathode ray tube are biased to cut-off the electron beam, upon triggering of the sweep circuit at the occurrence of the event to be recorded, there is a delay before the beam intensity is increased to the desired level and this degrades the brightness of the trace. The present invention eliminates unwanted light without decreasing the intensity of the electron beam and without deflecting the beam against the funnel portion of the tube to reflect onto the screen.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that Within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed and desired to be secured by Letters Patent of the United States is:

1. A cathode ray tube display system comprising:

a vacuous closed envelope having an observation screen formed therein,

said screen having a coating of phosphorescent material on its inner surface, an electron gun positioned within said tube for producing a stream of electrons and projecting an undeflected stream of said electrons along the axis of said envelope upon said material thereby producing a luminous spot in the center of said screen,

deflection means for normally directing said electron stream to a rest position near one edge of said screen and for causing said stream of electrons to traverse the screen in a manner representative of an electrical signal to be displayed, and

intercept means so positioned within said envelope as to intercept the stream of electrons only when the electrons are directed toward said rest position said intercept means comprising a cup-shaped member positioned adjacent said deflection means and radially displaced from the axis of said tube.

2. The cathode ray tube of claim 1 further comprising:

means for establishing a static electrical potential within said envelope, and

means for maintaining said electron intercept means at a positive electrical potential which is substantially equal to but slightly higher than the potential within said envelope in proximity to said intercept means.

3. The cathode ray tube of claim 4 further comprising:

means for maintaining said conical member at an electrical potential which is substantially equal to the potential of the tube in the proximity of said conical member.

4. The cathode ray tube of claim 1 wherein said cupshaped member is conical and electrically conductive.

References Cited UNITED STATES PATENTS 2,034,565 3/1936 Dreyer et al 31372 X 2,081,942 6/1937 Lubcke 31372 X 1,779,794 10/ 1930 Ackermann 315--20 2,066,037 12/ 1936 Hansell 31389 X 2,114,611 4/ 1938 Schlesinger 31520 X 2,163,256 6/1939 Du Mont 315--20 X ROBERT SEGAL, Primary Examiner US. Cl. X.R. 3l5--20 

